The present invention relates to marine jet drive shift control apparatus for accurately shifting of the jet drive into a neutral position.
Marine jet propulsion drive systems have recently been commercially developed for propelling relatively small recreational type vehicles and the like. Generally, the jet propulsion drive system is mounted to the aft or stern portion within the boat with an internal combustion engine driving a suitable pump unit for drawing water upwardly through a bottom intake opening and discharging of the water rearwardly through a transom-mounted jet nozzle unit. For forward movement, the jet is discharged, through a nozzle, longitudinally rearwardly of the boat. For reversing the direction of boat travel, a diverting means is employed for reversing the direction of the jet stream toward the front of the boat and thereby reversing the thrust created by such jet stream. Generally, a lid or gate is pivotally mounted to the forward thrust jet forming nozzle and is adapted to be moved downwardly into the jet path so as to deflect and redirect the jet downwardly into a reverse thrust jet forming nozzle. The gate may be a simple plate-like member pivotally mounted to the sidewalls of the forward jet nozzle and adapted to be pivoted downwardly into partial or complete overlying relationship to the discharge end of the forward jet nozzle. An internal gating system may also be employed for redirecting of the output of the pump flow from the forward forming jet nozzle to a reverse jet nozzle, such as shown in the pending application of William L. Woodfill, entitled, "MARINE JET DRIVE PROPULSION APPARATUS" which was filed with SER. No. 317,200, on DEC. 21, 1972, and which is assigned to the same assignee as the present application. In each construction, a remote control lever or other means is coupled to the gate for selective positioning thereof. Generally, a pivotally mounted lever is coupled to the gate by a suitable push-pull cable unit in the same general manner as remote controls for conventional propeller driven systems.
Generally, all marine jet drives include a continuously running pump which operates as long as the drive engine is operating. The thrust output is thus maintained and differs from the more conventional marine prop drive where the propeller is operatively disconnected from the engine to stop the propulsion or thrust forces. In order to hold a neutral setting for holding a jet driven boat stationary, the reversing gate means is positioned partially within the forward jet stream to establish a partial reverse jet which will just balance the forward jet thrust forces. This not only requires a reasonable sensitive setting of the control but the setting will tend to vary with the idle speed of the engine. When the shift control apparatus is formed for various jet drives on a production basis, the connection means will often not provide precise positioning of the gate means, to create equal and opposite forward and reverse thrust forces. Tailoring or customizing of the shift control connection to the engine is, therefore, generally required. Further, engine operation may tend to vary with time and require readjustment of the gate setting which will normally demand restructuring of the linkage.